This book was Herman Gorter's, a leading European Left Communist, response to Lenin's book criticizing the European Left as infantile. It outlines the differences and dangers of imposing a one size fits all approach to the communist revolution which the Communist International was doing.
“It would be a thousand times worse, that opportunism, with its devastating effect on the soul and the strength of the proletariat, should again slip in, than that the Left Wing should be too radical. The Left Wing, even though at times it goes too far, always remains revolutionary. The Left Wing will alter its tactics as soon as they are not right. The opportunist Right will grow ever more opportunist, will sink ever further into the morass, will corrupt the workers to an ever greater extent. Not in vain have we learned from twenty five years of struggle. Opportunism is the plague of the Labour movement, the death of the revolution. Opportunism has brought about all evils; reformism, the war, the defeat and the death of the revolution ... Opportunism is the cause of disaster.”